The present invention relates to vapor vent valves of the type employed in fuel tanks filled with volatile fuel for operating an internal combustion engine and for which it is desired to control the emission of fuel vapors during periods in which the engine is not operating.
Heretofore, fuel tank vapor vent valves have had problems with valve failure in arrangements where the rising level of the liquid fuel in the tank closes the valve outlet which is connected to the vent port through the wall of the tank. In particular, in such arrangements, upon withdrawal of fuel, problems have been encountered with the valve sticking and failing to reopen. A relatively large valve area is required to provide the desired vapor flow at low vapor pressures. Where a relatively low valve closing force is available from the float it has been necessary to use a relatively flexible and soft valve member which can be effectively seated on a valve surface with the available relatively low closing force.
A known float operated valve has employed a relatively thin flexible membrane valve member to effectuate closing with a relatively low closing force acting thereon. However, problems have been experienced with such valves upon the tank being completely filled with liquid fuel with the valve sticking closed or xe2x80x9ccorkingxe2x80x9d. Subsequently, when fuel is withdrawn and the float descends to a level intended to reopen the valve, the increased vapor pressure acts to continue to hold the membrane valve member closed on the valve seat.
Thus, it has long been desired to provide a way or means of ensuring a positive reopening of flow operated fuel vent valve having a relatively thin flexible valve member which seals readily upon the vent port seat with the available low closing forces from the float and which will positively reopen without sticking upon fuel withdrawal the float descending to the level wherein vapor venting is required.
The present invention solves the above described problem by providing a float actuated fuel vapor vent valve having a flexible elastomeric membrane type valve member caged for limited lost motion movement on the float assembly, with the upper portion of the cage having a downwardly extending projection for effecting localized peeling of the valve member from the valve seat upon lowering of the float assembly due to withdrawal of the liquid fuel from the tank. A preferred form of the float assembly has the cage formed with an inclined upper portion to effect peeling away of one side of the membrane from the valve seat thereby minimizing the force required to continue reopening of the valve on further lowering of the float assembly to ensure complete re-opening.